The present invention relates in general to a modular knee replacement system for a prosthetic joint, and more particularly to a system including a trochlear implant.
A knee joint connects three bones: the femur (thigh bone), the tibia (leg bone), and the patella (knee cap). Either through disease, injury, or pre-mature wear from mal-alignment, the knee joint can be damaged, and all or portions of the damaged joint surfaces may need to be replaced with a prosthesis. The most common prosthetic knee is referred to as a xe2x80x9ctotal knee replacementxe2x80x9d system because all knee joint surfaces are replaced. Typically the total knee replacement system includes a patellar prosthesis or implant, a femoral prosthesis or implant and a tibial, prosthesis or implant.
Different portions of the knee are referred to as compartments. For example, each condyle (rounded end of the femur) is a separate compartment. Other prostheses, called xe2x80x9cunicompartmentalxe2x80x9d replacements, can be used when only the medial (toward the body""s midline) compartment or the lateral (away from the body""s midline) compartment of the femoral-tibial surface needs to be replaced. The unicompartmental replacement systems have femoral and tibial prostheses but do not include a patellar implant. Currently available unicompartmental implant systems are designed to be modular and work with their total knee counterparts from the same manufacturer with respect to using the same instruments and same bone contour. When these unicompartmental prosthetic systems need to be replaced with a total knee system, both the femoral and tibial implants must be removed.
Less frequently, the surface of the knee joint compartment between the patella If, and the groove on the front of the femur the (trochlea) requires replacement. Several prosthetic implants are available which replace this part of the knee joint and are called xe2x80x9ctotal patello-femoralxe2x80x9d prostheses or implants. Typically the total patello-femoral prostheses have a patellar implant that is installed on the patella and another implant which replaces the portion of the femur which contacts the patella(the trachlea).
However, there is no total patello-femoral prosthetic system which is modular with any total knee system. Therefore, if a total patello-femoral prosthesis has been implanted, and because of further deterioration in the rest of the knee (possibly years later), during a then second operation both the trochlear implant and the patellar prosthesis must be removed even though the patellar prosthesis is functioning well. The only reason for removing said patellar prosthesis is that its articular surface would not now match or articulate smoothly with the new femoral prosthesis being implanted.
A prosthesis system which does not require replacement of the patella implant when replacing the patello-femoral prosthesis with a total knee prosthesis is desirable. In particular, a trochlear implant which is applied to the surface of the trochlear groove of the femur and which cooperates with the components of the selected total knee implant is desirable.
It is a primary object of the present invention to provide a prosthesis system which does not require replacement of the patella implant when replacing the trochlear implant with a full femoral implant.
It is another object of the present invention to provide a trochlear implant which cooperates with the components of the selected total knee implant system.
A more general object of the present invention is to provide a trochlear implant for a prosthetic joint that reduces the amount of bone removed for the implant.
It is yet another object of the present invention to provide a modular joint replacement system having interchangeable components.
In summary the present invention provides a prosthetic knee of the type which includes a femoral implant or a trachleas implant and a patellar implant. The femoral implant and the patellar implant have bearing surfaces that articulate with each other when the femoral implant and patellar implant move relatively. The trochlear implant has an articulation surface shaped to articulate with a portion of the bearing surface of the trochlear implant of the patellar implant. The articulation surface is substantially similar in shape to a portion of the bearing surface of the femoral implant such that the patellar implant is usable with either the femoral implant or the trochlear implant.
The present invention also provides a trochlear implant for use in a prosthetic knee. The trochlear implant mounts to the knee end of a femur and cooperates with a patellar implant mounted to the back side of a patella. The patellar implant is a component of a prosthesis system including a femoral implant for replacing the entire knee end of the femur. The trochlear implant has an articulation surface shaped to slidably receive a portion of the patellar implant. The articulation surface is substantially similar in shape to a portion of a surface of the femoral implant such that the patellar implant is capable of being used with either the femoral implant or the trochlear implant.
In addition, the present invention provides a method of knee replacement using a prosthetic knee system. A trochlear implant and a patellar implant are provided. The patellar implant cooperates with the trochlear implant and a femoral implant. The trochlear implant has an articulation surface shaped to slidably receive a portion of the patellar implant. The articulation surface is substantially similar in shape to a portion of a load bearing surface of a femoral implant. The patellar implant is installed in a patella in a knee. The trochlear implant is installed in the trochlear groove in the knee end of a femur bone.